[j-curve]

...because output resistors are evil!!

It's tempting to think that driving a set of headphones should be a walk in the park for an integrated amplifier. If the thing can pump 80 watts into 4 ohms then 10mW into 300 ohms shouldn't be much of a challenge.

Well, that's true, but unfortunately there's usually a nasty little component between the speaker terminals on the back panel and the headphone socket on the front panel, known as the output resistor. Kind of necessary in a way, since the effect of plugging a mono phono plug into the headphone socket or incompletely inserting a regular stereo plug can be a short circuit, which could have disastrous consequences if the volume was turned up and the amplifier's full power was available to the headphone socket. Melting the lugs to the plug would be quite likely. Fried output transistors could also be on the menu. Hence most manufacturers employ the cheapest method known to man - the output resistor - to limit the current.

Now if you're driving Ety 4P's and the output resistor happens to be around 80 ohms I guess you couldn't be much happier. If on the other hand you're pushing HD600's then you can expect to suffer loose lower-mids and a bass hump.

Having seen how a car battery can melt the end of a chrome vanadium spanner, I wouldn't advise wiring your own headphone socket direct to the speaker terminals. A better approach would be to use the existing front-panel headphone output with an external resistor divider, say 47 ohms and 4.7 ohms in series. The total 52 ohms goes across the headphone output, while the headphones are connected across the 4.7 ohm resistor. You need to turn the volume up a bit higher but you get a low impedance output to drive your phones.

 

[daycart1]

So I suppose that is how the ASL UHC and the Moretto HAP-4 work?

 

[gloco]

Quote:

Originally posted by j-curve Now if you're driving Ety 4P's and the output resistor happens to be around 80 ohms I guess you couldn't be much happier. If on the other hand you're pushing HD600's then you can expect to suffer loose lower-mids and a bass hump.

I regularly listen to my 580's out of my Receiver's headphone jack...i dont notice any bass hump due to the fact i keep the bass knob at 0. Have you tried this as well? I also listen to my Beyer 770-250's thru the jack and it sounds pretty sweet, a bit more crisp and refined than my cmoy.

 

[Dusty Chalk]

Quote:

Originally posted by daycart1 So I suppose that is how the ASL UHC and the Moretto HAP-4 work?

I'm pretty sure the ASL UHC-Sig is a transformer. Don't know about the Moretto.

 

[j-curve]

Quote:

gloco: i dont notice any bass hump due to the fact i keep the bass knob at 0. Have you tried this as well?

Sarcasm, I presume. Perhaps your receiver's jack has a low output impedance.

BTW, you don't need any fancy equipment to get a handle on the output impedance. Two sets of phones - one low impedance and one high impedance - plus a miniplug double adaptor will do the trick. While listening to the high impedance phones, plug in the low impedance phones to the double adaptor. If the volume goes down a lot, the output impedance is high. If the volume barely changes, it's low.

 

[gloco]

Quote:

Originally posted by j-curve Sarcasm, I presume. Perhaps your receiver's jack has a low output impedance.

I wasn't being sarcastic.

 

[Hirsch]

Quote:

Originally posted by Dusty Chalk I'm pretty sure the ASL UHC-Sig is a transformer. Don't know about the Moretto.

A transformer by any other name would sound as sweet...

 

[HD-5000]

How exactly does a resistor in the signal path degrade sound? Every piece of audio equipment has resistors in the signal path.

 

[markl]

Allow me to re-post this thread:
http://www4.head-fi.org/forums/showt...is+nothing+but

My hypothesis, which has yet to be authoritatively challenged, is that a "pre-amp" is no different from a "headphone amp", except for the addition of a headphone jack. A "pre-amp" has all the functionality of a "headphone amp" except that a "headphone amp" comes with a headphone jack instead of RCA outs. This allows you to listen to the pre-amp through a headphone instead of through an amp and speakers, or through the RCA outputs.

That's why so many "pre-amps" are such good "headphone amps", and vice-versa.

This begs the question-- if you wouldn't spend a measly $300 on a pre-amp, why would you spend a measly $300 on a head-amp? If you buy a $100 head-amp, you've essentially bought a $100 pre-amp.

Discuss...

Mark

 

[daycart1]

Well, some preamps need only a jack to be headamps (assuming the issues of current and impedence matching discussed in the other thread don't arise); e.g. Markl's Melos.

But don't some solid state preamps and integrateds have a separate op amp for the headphone jack?

 

[HappymaN]

Quote:

Originally posted by markl Allow me to re-post this thread: http://www4.head-fi.org/forums/showt...is+nothing+but My hypothesis, which has yet to be authoritatively challenged, is that a "pre-amp" is no different from a "headphone amp", except for the addition of a headphone jack. A "pre-amp" has all the functionality of a "headphone amp" except that a "headphone amp" comes with a headphone jack instead of RCA outs. This allows you to listen to the pre-amp through a headphone instead of through an amp and speakers, or through the RCA outputs. That's why so many "pre-amps" are such good "headphone amps", and vice-versa. This begs the question-- if you wouldn't spend a measly $300 on a pre-amp, why would you spend a measly $300 on a head-amp? If you buy a $100 head-amp, you've essentially bought a $100 pre-amp. Discuss... Mark

Yeah, but don't headphone amplifiers employ OP-amplifier chips? Isn't this a fundamental difference?

 

[daycart1]

Quote:

Originally posted by daycart1 Well, some preamps need only a jack to be headamps (assuming the issues of current and impedence matching discussed in the other thread don't arise); e.g. Markl's Melos. But don't some solid state preamps and integrateds have a separate op amp for the headphone jack?

 

[markl]

I'm saying that when you look at what a head-amp has to do to the audio signal vs. what a pre-amp has to do with the signal, it's virtually if not entirely identical.

Maybe a better analogy, which actually strengthens my argument, is that a head-amp is functionally equivalent to an "integrated amp" in the speaker world. It provides gain and the ability to amplify the signal. Some people have expensive integrateds or HT amps yet are encouraged to buy Total Airheads and such for their headphones. I question whether they really get any benefit. Perhaps the TA or a mini-META or Penguin or whatever can produce more power than the standard HT receiver jack, but isn't that counterbalanced by the superiority of the "pre-amp" portion of the HT reveiver?

Mark

 

[eric343]

FYI, the Melos' preamp-out sections and headphone-out sections are totally different... That's why it sounds so good! They actually put a lot of thought into the headphone out instead of just connecting it to the preamp out...


...you see, preamps are designed to drive fixed, very high impedance loads like the input of a power amplifier. Headphones are varying, low to medium (relatively speaking; 32 to 300 ohms is low to medium up against several thousand ohms) impedance loads. Whereas you could skip the Elantec buffer and just drive a nice high-impedance-input power amp from an AD8610 (one of the best opamps out there), woe to he who tries to drive headphones directly off it.

 

[markl]

Quote:

FYI, the Melos' preamp-out sections and headphone-out sections are totally different...

I have to disagree, and I speak as a know-nothing layman.

The Melos has one board on which all its pre-amp and headamp functionality is contained. There is one set of tubes that are in use whether I'm listening to the Headphone jack, or "listening" to the pre-outs. The difference is a small signal path that goes from the tubes to the headphone jack or goes from the tubes to the pre-outs. They are both controlled by the same volume control. The input signal comes in from the same set of jacks on the rear.

That's what I see when I open up my Melos. To the layman, it appears that the audio signal is "processed" by the exact same set of components and same circuit whether I'm listening to the headphone jack or the pre-outs.

What am I missing here?

Mark